Fuse-test for coefficient potentiometers



Oct. 22, 1968 ML II iMOTOR BUS A. G. TONNESSEN FUSE-TEST FOR COEFFICIENT POTENTIOMETERS Filed May 16, 1966 q fg 2 5 INVENTOR.

ALFRED G.TONNESSEN ATTORNEY United States Patent Office 3,407,293 Patented Oct. 22, 1968 3,407,293 FUSE-TEST FOR COEFFICIENT POTENTIOMETERS Alfred G. Tonuessen, Neptune, N.J., assignor to Electronic Associates Inc., Long Branch, N .J., a corporation of New Jersey Filed May 16, 1966, Ser. No. 550,359 Claims. (Cl. 235-493) This invention relates to coefiicient-setting potentiometers, and more particularly to the testing of fuses utilized with such potentiometers.

In analog computers, coefficient-setting potentiometers may be used to multiply computer voltages by a constant coefiicient. The potentiometers may be manually set by turning the shaft and obtaining an indication'of coefficient setting by observing the potentiometer dial or through the use of a digital voltmeter to read the coefiicient setting across a load connected to the potentiometer. In many large scale analog computers having a great many potentiometers it has been found advantageous to set the potentiometer by means of servo systems. By the use of such systems, potentiometers may be set automatically from a stored memory such as magnetic tape, paper tape, as well as from a digital computer. These sources of data provide a sequence of reference values and in turn each of the potentiometers are compared with a corresponding reference value. Specifically, in so setting a potentiometer, a desired reference voltage is compared with the coefficient previously set on a selected potentiometer. If the reference value and the previous value are not equal an error signal is produced. This error signal is amplified and then applied to a servo-motor to reposition the potentiometer until a null condition or zero error signal is obtained. In this manner, each of the potentiometers is automatically set in turn by an individual servo-motor.

, It has been known to provide each servo-set potentiometer with a fuse connected in a series circuit arrangement with its sliding contact or arm. The fuse provides protection for the potentiometer from errors caused by operators in patching the potentiometers or other computing elements of the analog computer. In practice, such fuses are blown quite often as a result of such patching errors and from other causes. Particularly in the case of servo-set potentiometers, for example, with control from an automatic digital computer program, the operator has considerable difficulty in recognizing that a fuse has blown. This difiiculty results from the fact that the potentiometer fuse when blown produces an open circuit and a potentiometer at null also appears as an open circuit. Thus, to the digital computer, a blown fuse of a potentiometerlappears the same as. a potentiometer at null.

Accordingly, an object of the present invention is a system for determining if a potentiometer fuse is open or blown when servo-setting that potentiometer.

Another object of the present invention is a fuse test system for servo-set potentiometers in which the test is performed at the time of servo-setting of the potentiometer.

In carrying out the invention in one form, there is provided a plurality of coefiicient potentiometers each set by an individual servo-motor. Each of the potentiometers has a first voltage supply of one polarity connected to one fixed terminal, a reference potential connected to its other fixed terminal, and a fuse connected to its sliding contact. A readout switching device is provided for each potentiometer and its corresponding servo-motor for connecting the associated fuse to a common conductor and for connecting the servo-motor to the output of a servo amplifier. Only one selected read out device is actuated at any one time to its circuit closing positions thereby to servo set only a corresponding potentiometer. A second voltage supply of the opposite polarity with respect to the first supply is connected to the common conductor. In this manner, there is provided a potential at the common conductor having an amplitude substantially between the potentials of the first and second supplies when the potentiometer fuse associated with the selected read out relay is continuous, viz, completes a circuit. The common conductor potential is substantially equal to the potential of the second supply and of the same polarity when the potentiometer fuse is blown. A- comparator is connected to the common conductor for producing a signal indi eating a blown fuse when the potential of the common conductor is substantially equal to the potential of the second supply and of the same polarity. A warning circuit, connected to the comparator and responsive to the indicating signal produces an alarm to the operator. In this manner, the operator is immediately advised that the coefficient potentiometer being servo set has a blown fuseI In a preferred from of the invention, a servo input relay is provided connected between the common condoctor and the input of the servo amplifier. The servo input relay is actuated to its closed circuit position by control means having an input connection to the comparator. The control means actuates the servo-input relay to initiate the servo-setting operation of a selected potentiometer. However, if the associated fuse is blown, a signal is applied from the comparator to the control means to switch the servo input relay to its open circuit position to prevent the potentiometer from being set to an erroneous position.

For further objects and advantages of the invention and for a more detailed development of the principles of the invention, reference is to be had to the following detailed description taken in conjunction with the accompanying drawing which schematically illustrates a fuse test system for servo-set potentiometers according to the invention.

Referring now to the drawing, there is shown a servoset potentiometer system for setting at least potentiometers 10 and 11 and comprising a servo amplifier system 12. Coefiicient-setting potentiomenters and in particular servo-set potentiometer systems are described in the literature and specifically at pages 2-3 et seq., Computer Handbook by Huskey and Korn, McGraw-Hill Book Company, Inc., 1962.

Each of the coefficient potentiometers 10 and 11 is servo-set by an individual servo motor 15 and 16 respectively. For purposes of illustration only two potentiometers 10 and 11 have been illustrated and it will be understood that the servo-set potentiometer system may include many more potentiometers each having its own respective servo motor. The potentiometers are set to potentials set on a precision voltage divider 18, which may be operated for example by a digital computer or by an operator on a keyboard.

For ease of explanation, divider 18 is illustrated as having one end connected to a battery 19 and its other end connected to ground. The movable contact of divider 18 is connected by way of fixed contact 20a and a movable contact 20b of a relay 20 to a center tap 24a-of a primary winding of a transformer 24.

It will be assumed that divider 18 has been operator set and it is desired to set coefiicient potentiometer 10 to the potential of divider 18. Thus, potentiometer 10 read out relay 25 is actuated to its circuit closing position thereby to actuate its movable contacts 25a and 25b to engage its fixed contacts 25c and 25d, respectively. Potentiometer 10 has one end connected to a positive supply 26 and its other end connected to ground. The movable or sliding contact or brush 10a of potentiometer 10 is connected by way of a fuse 28, contact 25d, movable contact 25b and through fixed contact 20c and movable contact 20d of relay 20 tothe v ibrating chopper arm 30a of modulator 30 of servo amplifier 12. Aj 'read out relay system is described in detail in my copending-application entitled Readout System, Ser. No. 455,470 filed May 13, 1965 and assigned to the same assignee as the present invention. Fuse 28 may be any of the fast acting types well known in the art utilized for ,coeflicient potentiometer applications such as ampere; If the potential produced at the sliding contact of potentiomcter and the potential produced by'the precision reference divider. 18 are not identical, then the potential applied to the center tap 24aland the movable contact 300. provides a difference or error potential which is modulated by, the movable contact 30g. It will be-..understood that when .the reference voltage and the potentiometervoltage are identical a nullis produced and there is no loading of the potentiometer bymodulator 30. The modulated signal is applied from the primary to thesecondary of transformer 24 and is amplified by amplifier 38 ofservo amplifier system 12,

The output -of amplifier 38 is applied to a primary of transformer 40, the secondary of which is connected to fixed terminals 35b and 35c of demodulator chopper 35. In this manner, the error signal is demodulated to a DC potential which is applied through a DC. amplifier 41 and by way of conductor 42, movable motor contact 25a, 'fixed motor contact 250 of read outrelay 25 to the servo motor 15. Since it has been assumed that motor contact 25a is in a circuit closing position then motor is energized to drive the sliding. contact or brush 10a of potentiometer 10 until a null is reached. It will now be under,- stood that with 25 and 27 actuated to a circuit closing position that potentiometer 10 is servo-set to the value set on divider 18. In similar manner,- with servo input relay energized and read out relay 27 energized, then potentiometer 11 may be servo set until a null is reached with the value set on potentiometer 11 equal to the-setting ofv divider 18.

In order to actuate servo input relay 20 it is connected to the l-output of a set flip-flop 44. Accordingly, to set its contacts to their circuit closing position, flip-flop 44 is set by means of a connection from its set terminal through a push button switch to the positive side of a battery 45. Simultaneously, with the energization of relay 20, the fuse test circuitry is actuated to determine if the fuse of the potentiometer being servo set is blown. Specifically, it will again be assumed that read out relay has been energized with its contacts in their circuit closing position and set push button 44a is actuated thereby to set flip-flop 44 to actuate servo inputrelay 20. In addition, the l-output of flip-flop 44 is connected by way of a conductor 48 to actuate a three millisecond monostable multivibrator or one-shot 50. The output of one-shot 50 is connected through winding 52a of a fuse test relay.52 and to the positive side of a battery 54, the negative side of which is connected to ground.

Accordingly, upon actuation of one-shot 50, relay winding 52a is energized for three milliseconds, thereby to actuate movable arms 52b and 52c, of relay 52 to their circuit closing position. With-arms 52c engaging fixed contact 52d, a circuit may be traced from the positive side of potentiometer battery 26 through potentiometer 10 to movable contact 10a, fuse 28, arm 25b, and then by way of a common conductor 55 through contact 52c and a resistor 56-to the negative side of a testing battery or source of supply 57, the positive side of which isconnected to ground.

Thus, in accordance with the invention, at. the time of energization of the servo input relay 20, a fuse test relay 52 is actuated to apply a negative supply to one side of fuse 28 while the other side of fuse 28 is connected to the positive potentiometer supply 26. If fuse 28 is open or blown, then common connector 55 will be driven to a potential substantially equal to the potential of battery 57 and of the same polarity. On the other hand, if fuse 28 is not blown, then the magnitude of the potential of conductor will be somewhere between the positive potential of battery 26 and the-negative potential of battery 57, depending onthe setting of potentiometer 10 and the value of resistor 56. It will understood that relay 52 may be actuated prior to the timethatfservo-input relay 20 is actuated so that the fusetes't may'take'place somewhat prior to the time of the servo-setting of potentiometer 10.

In order to determine the polarity and, potential of conductor 55, there is provided a comparator circuit connected tothe movable'contact 5 2b of relay 52.,With relay 52 energized, the negative supply 57- isconnected to common conductor 55 and contact 52b engages fixed contact 52e thereby also connecting conductor.55 to comparator circuit 60 by way of an input resistor61. Comparator 60 comprises a pair of switchingtransistors 63 and 64,- both ofthe NPN type and each having their emitters connected to ground. The collectors of transistors 63.and 64 are connected by way of respective resistors 66 and 67 to the positive sideof a supply battery'68, the negative side of which is connected to ground. In addition, the base of transistor 63 is connected by way of a bias resistor 70 tothe positive side of battery 68. Accordingly, it will be understood that transistor 63 is maintained normally on and transistor 64 having its base connected to the collector of transistor 63, is maintained normally otfe The collector ofv transistor 64 is connected to the set input of an error flip-flop 72 which in the normal condition for the comparator 60 is in its O-state. 1

Accordingly, when fuse 28 is blown or open, conductor 55 is at substantially the negative potential of supply 57 which. is applied to the base of transistor63thereby to apply a positive-going potential to transistor 64. Thus, transistor 64 is turnedon and an actuating zero volt signal is applied to the set input of flip-flop 72. Flip-flop 72 is adapted to beswitched to its l-state by said zero volt signal and upon being switch to apply a l-state signal from its l-output to a flashing or warning circuit 74. The l-state signal to flashing circuit 74 is effective to produe a flashing alarm signal which is applied to one end of a lamp 75, the other end of which is connected to ground. v

In addition to actuating the flashing circuit 74 the l-side of flip-flop 72 is also connected by way of a" conductor 77 to the reset input of flip-flop 44. Accordingly, if fuse 28 is blown a l-state signal is applied to flip-flop 44 to reset it, thereby deenergizing servo input relay 20. Relay 20 may have been actuated to a circuit closing position for a short period of time before it is deenergized but that short period is insuflicient to produce an error in potentiometer 10. At the end of the three millisecond time duration of the quasi-stable state of the monostable multivibrator 50, relay 52 is deenergized and contacts 52b and 520 are actuated to their circuit opening position. However,flashing circuit 74 continuesto actuate the bulb 75 to indicatea blown fuse, until the operator turns off the flashing circuit.

Thus, in accordancewith the invention, if a fuse is blown, the operator is .warned as by a flashing circuit and the servo-input relay is deenergized so that error signals are not applied to the servo-motor 15.

If fuse 28 is not blown and completes its circuit and the potential at conductor 55'is at some potential between the potentials of the supply batteries 26 and 27 and this intermediate-potential is applied to the base of transistor 63. This potential is not sufliciently negative-going to turn off the normally on transistor 63 and therefore transistor 63 as well as 64 are maintained in their normal states. Accordingly, flip-flop 72 is not actuated to energize the flashing circuit. 74 or to reset flip-flop 44. Thus, at the end of the three millisecond time delay of the one-shot 50, relay 52 is deenergized and the fuse test system of the present invention has had no effect upon the operation of the servo-set system.

It will be understood that in accordance with the invention, that as each of the read outrelays 25, 27, etc., is actuated in turn, its respective potentiometer fuse 28, 28a, etc., is tested by the fuse testing system. If a coefficient potentiometer fuse is blown, a warning device is actuated and the servo-input relay is deenergized.

It will be understood by those skilled in the art that the above described detailed embodiment is meant to be merely exemplary and that it is susceptible to modification and variation without departing from the spirit and scope of the invention. For example, the flashing circuit for bulb 75 may be replaced by other alarm or warning devices such as buzzers and bells. In addition, one servo motor may be used for a group of potentiometers by means of pulleys and bells and individual engaging solenoid is used for each potentiometer.

What is claimed is:

1. An analog computer including a plurality of coefficient potentiometers each having at least a first and a second fixed terminal and a sliding contact and each of said potentiometers having its sliding Contact set by an individual servo motor comprising each of said potentiometers having a first source of supply of one polarity connected to said first fixed terminal and a reference potential connected to said second fixed terminal,

each of said potentiometers having a fuse connected to said sliding contact,

ser-vo amplifier means having an input and an output,

first relay means for each of said potentiometers and its associated servo motor for connecting the associated fuse to a common conductor and for connecting said servo motor to said output of said amplifier means when said first relay means is actuated to a circuit closing position,

means for actuating to a closed circuit position only a selected one of said first relay means at any one time,

means for connecting said common conductor to said input of said amplifier means whereby the potentiometer associated with a selected first relay means is set by its respective servo motor,

a second source of supply of the other polarity with respect to said first source of supply being connected to said common conductor thereby to provide a potential'at said common conductor (1) substantially between the potentials of said first and second sources of supply when said potentiometer fuse associated with a selected first relay means is continuous and (2) substantially equal to the potential of said second source of supply and of the same polarity when said potentiometer fuse associated with a selected first relay means is open,

comparator means connected to said common conductor for producing a signal indicating an open fuse when the common conductor is substantially equal in potential to that of said second source and of the same polarity, and

warning means connected to said comparator means and responsive to said signal for producing an alarm indicating an open fuse.

2. The analog computing system of claim 1 in which said connecting means comprises second relay means for connecting said common conductor to said input of said amplifier means, control means connected between said comparator means and said second relay means for operating said second relay means to an open circuit position when said comparator means produces a signal indicating an open fuse.

3. The analog computing system of claim 2 in which there is provided third relay means connected (1) between said second source of supply and said common conductor and (2) between said common conductor and said comparator means and being actuated to a closed circuit position only for a predetermined fuse test time.

4. The analog computing system of claim 3 in which there is provided timing means connected to said control means for producing an energizing signal for a predee termined time duration after the operation of said second relay means to a closed circuit position, and means for applying said energizing signal to said third relay means for actuating said third relay means to its closed circuit position only during said predetermined time duration.

5. The analog computing system of claim 2 in which said control means comprises a flip-flop circuit having one input terminal connected to said comparator means and another input terminal connected to a switch for setting said flip-flop circuit, and in which said second relay means comprises a first relay contact connected between said common conductor and said input of said amplifier means and a second contact connected between a reference supply and said input, and means connecting one of the outputs of said flip-flop circuit to said second relay means for actuating said relay means to its closed circuit position when said flip-flop circuit is set.

6. A fuse testing system for a plurality of servo-set coefiicient potentiometers each being protected by a fuse connected in circuit and each having at least a first and a second fixed terminal and a sliding contact comprising each of said potentiometers having a first supply of one polarity connected to said first fixed terminal and a reference potential connected to said second fixed terminal,

servo amplifier means having an input and an output connected to a servo motor,

first relay means for each of said potentiometers for connecting its sliding contact to a common conductor when said first relay means is actuated to a closed circuit position,

means for actuating to a closed circuit position only a selected one of said first relay means at any one time,

second relay means for connecting said common conductor to said input of said amplifier means whereby the potentiometer associated with a selected first relay means is set by said servo-motor,

a second supply of the other polarity with respect to! said first source of Supply being connected to said common conductor thereby to provide a potential at said common conductor (1) substantially between the potentials of said first and second supplies when said potentiometer fuse associated with a selected relay means is not open and (2) substantially equal to the potential of said second supply and of the same polarity when said potentiometer fuse associated with a selected first relay means is open, and

comparator means connected to said common conductor for producing an operator alarm indicating an open fuse when the common conductor is substantially equal in potential to that of said second supply and of the same polarity.

.7. The fuse testing system of claim 6 in which said second relay means is operable between a closed circuit and an open circuit position for connecting said common conductor to said input of said amplifier means when in a closed circuit position, control means connected between said comparator means and said second relay means for normally operating said second relay means to a closed circuit position and for operating said second relay means to an open circuit position when said comparator means produces said operator alarm.

8. The fuse testing system of claim 7 in which there is provided third relay means connected in circuit between said second supply and said common conductor and between said common conductor and said comparator means and being actuated from an open circuit to a closed circuit only at a predetermined fuse test time when a selected first relay means is in a closed circuit position.

9. The fuse testing system of claim 8 in which there 7 v is provided timing means connected to said control means for producing an energizing signal 'for a predetermined time duration after actuation of said second relay means to a closed circuit position and means for applying said energizing signal to the third relay means for actuating said third relay means to its closed circuit position during said predetermined time duration. i

10. The analog computing system of claim 9 in which 'said control means comprises a flip-flop circuit having one input terminal connected to said comparator means and another input terminal connected to a switch for setting said flip-flop circuit, and inwhich said second relaymeans comprises a first relay contact connected between said common conductor and said input of said amplifier means and a second contact connected between a 'refe'r- 15 J. F. RUGGIERO, Assistant Examiner.

ence supply and said'input, and means connecting one of the outputs of said flip-flop circuits to'said second relay means for actuating said second relay means to its closed circuit position when said flip-flop circuitis set.

' References Cited I UNlTED STATES, PATENTS MALCOLM A; MORRI'PSON, Primary Examiner. 

1. AN ANALOG COMPUTER INCLUDING A PLURALITY OF COEFFICIENT POTENTIOMETERS EACH HAVING AT LEAST A FIRST AND A SECOND FIXED TERMINAL AND A SLIDING CONTACT AND EACH OF SAID POTENTIOMETERS HAVING ITS SLIDING CONTACT SET BY AN INDIVIDUAL SERVO MOTOR COMPRISING EACH OF SAID POTENTIOMETERS HAVING A FIRST SOURCE OF SUPPLY OF ONE POLARITY CONNECTED TO SAID FIRST FIXED TERMINAL AND A REFERENCE POTENTIAL CONNECTED TO SAID SECOND FIXED TERMINAL, EACH OF SAID POTENTIOMETERS HAVING A FUSE CONNECTED TO SAID SLIDING CONTACT, SERVO AMPLIFIER MEANS HAVING AN INPUT AND AN OUTPUT, FIRST RELAY MEANS FOR EACH OF SAID POTENTIOMETERS AND ITS ASSOCIATED SERVO MOTOR FOR CONNECTING THE ASSOCIATED FUSE TO A COMMON CONDUCTOR AND FOR CONNECTING SAID SERVO MOTOR TO SAID OUTPUT OF SAID AMPLIFIER MEANS WHEN SAID FIRST RELAY MEANS IS ACTUATED TO A CIRCUIT CLOSING POSITION, MEANS FOR ACTUATING TO A CLOSED CIRCUIT POSITION ONLY A SELECTED ONE OF SAID FIRST RELAY MEANS AT ANY ONE TIME, MEANS FOR CONNECTING SAID COMMON CONDUCTOR TO SAID INPUT OF SAID AMPLIFIER MEANS WHEREBY THE POTENTIOMETER ASSOCIATED WITH A SELECTED FIRST RELAY MEANS IS SET BY ITS RESPECTIVELY SERVO MOTOR, 